Until now, titanium, titanium nitride, silicon-containing titanium nitride and the like have been used as a raw material for a wiring barrier film in a semiconductor device. Furthermore, silicon oxynitride (SiON) and alumina (Al2O3) are used as main raw materials in a DRAM capacitor dielectric of a semiconductor device which has heretofore been developed. Moreover, silica (SiO2) has been used as a main raw material in a gate insulating film of a semiconductor device. However, miniaturization of a device is required in the next generation semiconductor in order to meet high performance, and a material having further high dielectric constant is required in a raw material of a capacitor dielectric and a gate insulating film. At the present time, titanium oxide, zirconium oxide, hafnium oxide and a composite oxide containing those metals, aluminum and the like are noted as a novel material used in those sites.
A formation method of a thin film now used as a semiconductor element includes a physical vapor deposition method (PVD method) by sputtering, and a chemical vapor deposition method (CVD method). However, in a semiconductor production in the next generation or later, it is required to form a uniform and thin film on a surface having a complicated three-dimensional structure of a miniaturized element. PVD method is not suitable as a method of forming a uniform thin film on a surface having concave and convex, i.e., a method of preparing a thin film having good step coverage. For this reason, a thin film formation method by CVD method which sends a raw material in a form of a gas to a reaction chamber and decomposes the same to deposit a thin film, or an atomic layer deposition method (ALD method) which adsorbs a raw material on a substrate surface and decomposes the same to deposit a thin film is investigated.
In a semiconductor element production, a raw material that has appropriate vapor pressure and thermal stability and can vaporize in a stable supply amount is selected as a raw material for forming a thin film by CVD method or ALD method. Furthermore, it is one of necessary conditions that a material can be film-formed with uniform thickness on a surface having a complicated three-dimensional structure. Moreover, it is preferred that a raw material is liquid when supplied.
Titanium tetrachloride TiCl4, tetrakisamide complex Ti(NRR′)4 (R and R′ are a methyl group or an ethyl group) and the like are investigated as a raw material that forms a titanium thin film, a titanium nitride film and a silicon-containing titanium nitride film, used in a wiring barrier and an electrode film of a capacitor by CVD method or ALD method.
Chlorine remains in a thin film formed by TiCl4 of the above raw materials, and high temperature is required to completely remove chlorine. For this reason, TiCl4 is not suitable as a raw material for forming a thin film on a portion which requires film formation at low temperature and a portion to which residual chlorine adversely affects.
It is known that Ti(NRR′)4 has extremely high reactivity to water and reacts with a slight amount of water contained in a carrier gas, a reaction gas or the like used in film formation, and oxygen is liable to be incorporated in a film formed. For example, it is reported that 10 atm % or more of oxygen is contained in a titanium nitride thin film formed by a remote plasma ALD method using tetrakis(dimethylamido)titanium Ti(NMe2)4 as a raw material (Non-Patent Document 1). A thin film containing oxygen has high specific resistance value, and therefore, does not satisfy the demand characteristics of a barrier layer. In other words, those tetrakisamide complexes are not suitable as a raw material for barrier layer formation.
On the other hand, tetraisopropoxotitanium Ti(OiPr)4, (bisisopropoxo)(bis(2,2,6,6-tetramethylheptanedionato))-titanium Ti(OiPr)2(THD)2 tetrakis(2-methoxy-1-methyl-1-propoxo)titanium Ti(MMP)4 and the like are investigated as raw materials for forming a titanium oxide thin film and a titanium-containing oxide thin film used in a capacitor dielectric film by CVD method of ALD method.
Where it is attempted to form a thin film using Ti(OiPr)4 as a raw material, Ti(OiPr)4 has extremely high reactivity to water, and as a result, there is the possibility that contamination of a slight amount of water vapor into a piping in an apparatus forms fine powder of titanium oxide, thereby clogging a pipe. Furthermore, where Ti(OiPr)4 is blown to a substrate and decomposed thereon, an alcohol is generated, and the alcohol is decomposed into water and an alkene. Water reacts with undecomposed Ti(OiPr)4 to form a fine powder of titanium oxide, and the fine powder is adhered to a film formation chamber and a discharge port, resulting in the decrease of productivity. For this reason, Ti(OiPr)4 is not suitable as a raw material for the formation of a thin film used in a semiconductor element (see Patent Document 1).
Where a thin film is formed using Ti(OiPr)2(THD)2 or Ti(MMP)4, particularly where a titanium-containing composite oxide thin film is formed by CVD method, volatilization properties and decomposition properties of those to other metal supply source raw materials greatly differ, and as a result, there was the problem that it is difficult to control a composition of a thin film, thereby decreasing productivity.
There are examples that ZrCl4, Zr(acac)4 (acac=acetylacetonate), Zr(tmhd)4, (tmhd=2,2,6,6-tetramethyl-3,5-heptanedionate) and the like are used as raw materials of a zirconium oxide thin film or a zirconium-containing composite oxide thin film by CVD method or ALD method. However, those materials each have low vapor pressure, and are not preferred as a raw material for the synthesis of a thin film by CVD method or ALD method. Zr(OtBu)4 (tBu=tert-butyl) has good vapor pressure, but has the disadvantage that a film formation temperature is high. Tetrakisamide complexes Zr(NRR′)4 (R and R′ are a methyl group or an ethyl group) are also investigated. However, those tetrakisamide complexes are slightly poor in thermal stability, and are not preferred as a raw material for the synthesis of a thin film by CVD method or ALD method (Non-Patent Document 2).
HfCl4, Hf(acac)4 (acac=acetylacetonate), Hf(tmhd)4 (tmhd=2,2,6,6-tetramethyl-3,5-heptanedionate), Hf(OtBu)4 (tBu=tert-butyl), and additionally tetrakisamide complexes Hf(NRR′)4 (R and R′ are a methyl group or an ethyl group) are investigated as raw materials of a hafnium oxide thin film or a hafnium-containing composite oxide thin film by CVD method or ALD method. Problems of those raw materials are described in Non-Patent Document 3.
Of the above raw materials, HfCl4 has low volatility and requires high temperature to form an oxide film. Therefore, HfCl4 is not suitable as a raw material for the formation of a thin film used in a semiconductor element. HfCl(tmhd)3 and HfCl2(tmhd)2 containing a chlorine atom are investigated (see Patent Document 2), but their vaporization temperature is high and those are not satisfactory raw materials.
An example that a hafnium oxide thin film was formed by ALD method using tetrakisamide complexes Hf(NRR′)4 as a raw material is reported (Non-Patent Document 2). However, it is described in Non-Patent Document 2 that thermal stability of tetrakisamide complexes is low, and it is reported that, for example, tetrakis(dimethylamido)hafnium Hf (NMe2)4 gradually decomposes at 90° C., and tetrakis(ethylmethylamido)hafnium Hf(NMeEt)4 gradually decomposes at 140° C. As a result that the present inventors actually investigated thermal stability of Hf(NMeEt)4 by heating the same at 150° C. for 120 hours, it was confirmed that 78% of Hf(NMeEt)4 decomposes. In other words, it is difficult to say that those tetrakisamide complexes have sufficient thermal stability as an industrial raw material for thin film formation.
An alkyl aluminum compound such as trimethyl aluminum, and an amide aluminum compound such as hexakis-(diethylamido)dialuminum have been investigated as an aluminum compound for forming a composite oxide thin film of aluminum and titanium, zirconium or hafnium. However, the alkyl aluminum is a spontaneously combustible substance or a water-prohibiting substance, and instantaneously combusts by the contact with a slight amount of air, thus being dangerous. To use those substances, there is the problem that specific facilities must be provided. Furthermore, an amide aluminum compound has a dinuclear structure, and as a result, vapor pressure thereof is low. Therefore, the amide aluminum compound is not suitable as a raw material for thin film formation by CVD method or ALD method.
A trialkyl gallium is investigated as a raw material in forming a gallium nitride thin film or a gallium arsenic thin film for use as a semiconductor. However, those are a spontaneously combustible substance or a water-prohibiting substance, similar to a trialkyl aluminum, and to use those, there is the problem that special facilities must be provided.
Non-Patent Document 1: Journal of The Electrochemical Society, 152, G29 (2005)
Non-Patent Document 2: Chemistry of Materials, 14, 4350 (2002)
Non-Patent Document 3: Journal of Materials Chemistry, 14, 3101 (2004)
Patent Document 1: JP-A-2004-196618
Patent Document 2: JP-A-2003-137551